Proteases and protease inhibitors are known to play important roles in tumor invasion and metastasis (Liotta et al., Cell 64:327, 1991). Proteinase degradation of the extracellular matrix is a prerequisite to invasion and metastasis. Proteinase inhibitors function to prevent this process.
Maspin is a serpin expressed in normal human mammary epithelial cells (Sager et al., U.S. Pat. No. 5,470,970; Zou et al., Science 263:526, 1994). Maspin expression in these cells decreases with increasing malignancy, and its expression is lost in metastases (Zou et al., supra).
Maspin, whether expressed in tumor transfectants or added as recombinant maspin from outside tumor cells, inhibits invasion in a Boyden chamber assay (Sheng et al., J. Biol. Chem. 269:30988, 1994). In addition, maspin protein has been shown to inhibit mobility of tumor cells (Sager et al., Curr. Top. Microbiol. Immunol. 1:51, 1995).